According to AISI Material Standards as well as to Stahl-Eisen-Werkstoffblatt (Steel-Iron Material Bulletin), the commercially available high-speed steels are in the following alloy range:
______________________________________ 0.5 to 3.0% C 0 to 12.0% Co 3.0 to 5.0% Cr 0.5 to 12.0% Mo 1 to 10.0% V 1 to 19.0% W Remainder Fe. ______________________________________
They are predominantly melted in an arc furnace and are further processed by forging, rolling and drawing. The output decreases steeply with increasing alloy content. As a result, tempered high-speed steels have not appreciably more than 30% by volume of carbide. If the processing leads via semifinished material, the alloy content is limited by the hot workability. This is not true to the same extent for fabrication processes, in which parts are made directly, such as sintering as well as pressure sintering and casting as well as cladding by hard-facing, spraying or immersion. The reference to the last-mentioned special processes indicates savings of alloying elements can be achieved by composite action of different materials. According to general opinion, a base material of unalloyed or alloyed structural steel with a strength of 800 N/mm.sup.2 is sufficient. In the investigations pertaining to the following application, micro-alloyed perlitic steel such as Material 49 MnSiNb 3 with a hardness of about 248 HV 10 has proven itself as base material.
High-speed steels are distinguished by high tempering stability and hot hardness as well as high wear resistance. In the average, the chromium content of high-speed steels is 4%. In a ferrite-free, low residual austenite, martensitic structure, this chromium content in conjunction with carbon ensures sufficient hardness and toughness. The hot hardness is increased by finely distributed precipitates of special carbides of the elements tungsten, molybdenum and vanadium taking place in the solid solution. The carbides formed during the solidification of the melt and in the solid state, embedded in the martensitic base matrix provide the high wear resistance. A particularly pronounced influence on the wear characteristics is ascribed to the relatively hard vanadium carbides.